It is perceived that there is a current and urgent need for air-monitoring devices that are easy to operate, can be manufactured in large quantities, can detect and identify as many hazardous agents in the atmosphere as possible, and are highly portable so that they can be readily and easily deployed wherever and whenever required and can be highly responsive to the presence of selected particles both in the open air and inside buildings, in mass transport vehicles such as aircraft, ships, trains and buses as well as being available for personal use. It is also a requirement that such devices can identify these hazardous agents within a sufficiently short time frame that remedial action can be taken before they can have any serious effect, both in the military and non-military environments.
Previous proposals have been put forward to provide particle separation for particles as small as the sub-micron level (see for example “Particles separate doing the Tango” Biotechnology July 2004, “Continuous Particle Separation Through Deterministic Lateral Displacement” by L. R. Huang et al. Science, May 14, 2004). A further study, among others, is to be found in “Virtual Impactors: A Theoretical Study” by V. A. Marple & C. M. Chien published 1980 in Environmental Science & Technology by the American Chemical Society.
Whilst such separators are known and have been proposed for separating extremely small particles, they are not suitable as separators of monitoring devices which are required for the separation and identification of microbial or bacteriological or like particles, and are not readily deployable in numbers.
The fundamental reason for this is that known particle separators are substantial, can only deal with small volumes of air or other gases in a given time frame and are primarily concerned with separation, but not necessarily with the preservation of the integrity of, the particles so separated, so that a pathogen, virus, germ or the like can be subsequently identified, due to collision of such particles as they are being separated and collected. Indeed, in the prior art, collision is identified as a definite result of the structure and operation of the separator.
Collision may occur in the particle stream or with walls of known separators, or both. If this occurred in separating bacteria and the like, the ability to identify that bacterium would be seriously impaired due either to damage to the bacterium, thereby potentially altering its own structure, or due to cross contamination. Consequently, known particle separators are unsuitable for use in separating and collecting particles which can be damaged by impact.
We have therefore developed a particle separator in which the potential risk of such damage is minimised. This has been achieved by analysis of a range of bacteria, viruses etc. as to size and mass, and an understanding of the optimisation of the air flow which will permit separation of such particles without any significant collision between them.
Generally speaking, in ambient air, particles exist that are of a range of less than 50 microns. Larger particles in the atmosphere generally tend to settle and do not remain in the atmosphere. Below the 50 micron level, atmospheric particles can usually be classified into three size ranges, namely 20-50 microns, 2-20 microns and below 2 microns. Micro-organisms such as bacteria, germs, viruses and the like are normally considered to be at the lower end of the overall range, though some noxious and poisonous materials may exist in the sub 40 micron, and in particular the 2-20 micron, range. For this reason, it may also be advantageous to consider the centre range as comprising more than one ‘sub-range’. For a separator of a ‘universal’ detector of chemical and/or biological agents, it is most important that as many pathogenic and/or toxic substances are detected as is possible, which is to say without damage thereto such as would remove the ability to identify them.